Heparin is the most widely used anticoagulant for the prevention and initial treatment of venous thromboembolism, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). PE is estimated to result in more than 300,000 hospital admissions per year and is responsible for approximately 50,000 to 250,000 deaths annually in the United States alone. There are numerous indications approved and unapproved that involve use of heparin products, both fractionated and unfractioned. Usually, the goal of the therapy is to treat or prevent a thrombotic event.
Heparin is a potent anticoagulant whose chemical composition includes a mixture of repeating disaccharide units, composed of glucosamine and either L-iduronic or D-glucuronic acid. Heparin is a naturally occurring glycosaminoglycan most frequently isolated commercially from cow lung and porcine intestinal mucosa. It is sulfated, anionic, and highly acidic.
Heparin inhibits reactions that lead to the clotting of blood and the formation of fibrin clots also known as thrombus. It inhibits several activated coagulation factors, in particular, factor Xa and factor IIa, by binding to the plasma protease inhibitor antithrombin III. It is partially metabolized by desulphation and depolymerization.
Heparin includes both unfractionated and low-molecular-weight heparin, e.g., dalteparin sodium, enoxaparin, tinzaparin. Heparins are indicated for prophylaxis of ischemic complications in unstable angina and non-Q-wave mycordial infarction, prophylaxis of deep vein thrombosis (DVT) in patients following hip or knee replacement surgery, and prophylaxis of DVT in patients following abdominal surgery in patients at risk for thromboembolic complications. Abdominal surgery patients at risk include those who are over 40 years of age, obese, undergoing surgery under general anesthesia lasting longer than 30 minutes or who have additional risk factors such as malignancy or a history of DVT or pulmonary embolism. Heparins are also indicated for prophylaxis of DVT in medical patients with severely restricted mobility during acute illness, and treatment of DVT with or without pulmonary embolism.
The anticoagulant effect of heparin requires the presence of antithrombin III to facilitate the formation of a 1:1 complex with thrombin. The rate of thrombin-antithrombin III complex formation is increased 1,000-fold by heparin which serves as a catalytic template to which both the inhibitor and thrombin bind. Binding of heparin also induces a conformational change in antithrombin, making the reactive site more accessible to thrombin. Antithrombin binds to heparin via sulfate groups on a specific pentasaccharide sequence found in about 30% of heparin molecules. The heparin-antithrombin III complex can also inhibit activated Factors IX, X, XI, and XII. Once thrombin binds to antithrombin, the heparin molecule is released from the complex. When, for example, the concentration of heparin in plasma is about 0.1 to 1.0 IU/mL, thrombin, Factor IIa, and Factor Xa are rapidly inhibited by antithrombin III. The result is an increase in blood coagulation time, as measured by activated partial thromboplastin time (aPTT), thrombin time, anti-Factor IIa, and anti-Factor Xa activity.
Presently, heparin is administered parenterally, either by continuous or intermittent intravenous infusion or by deep subcutaneous injection. Heparin alone is not well absorbed through the gastrointestinal tract.
U.S. Pat. No. 6,458,383 discloses a delayed release pharmaceutical dosage form for oral administration of a hydrophilic drug. The dosage form comprises low molecular weight heparin, a bile salt or bile acid, and at least one surfactant selected from hydrophilic surfactant, a lipophilic surfactant, and mixtures thereof.
There remains a need for heparin pharmaceutical compositions that can be administered orally and provide an increased heparin response, i.e., an oral heparin administration that can traverse the gastrointestinal tract and provide increased bioavailability. Such a composition would provide a more convenient dosage method for patients receiving heparin. Oral heparin would also increase patient compliance, particularly for patients requiring prophylactic therapy to prevent major venous thromboembolic events. The fact that injections and needles are not required is appealing to patients and can reduce infections due to the disruption of the integrity of the skin by injections.